This section provides background information to facilitate a better understanding of the various aspects of the invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
When using downhole tools, it is often necessary to pump different types of fluids downhole. In the case of downhole milling or drilling, nitrogen and water are pumped through a single coiled tubing and through a tool string that includes a positive displacement motor. The nitrogen is used to provide underbalanced pressure to the well which pushes milling or drilling debris to the surface when a well lacks sufficient pressure to overcome the hydrostatic pressure in the wellbore. Water is pumped downhole to run the motor. Nitrogen can cause accelerated deterioration of the rubber in the stator of the positive displacement motor. By pumping water with nitrogen in it downhole, there is a risk that the well can become choked off with fluid.